1. Field of the Invention
This invention relates to a process for producing a light-receiving member having a sensitivity to light (which herein refers to light in a broad sense and indicates ultraviolet rays, visible rays, infrared rays, X-rays, .gamma.-rays, electromagnetic waves, etc.), a deposited film forming apparatus used to produce the light-receiving member, and a method for cleaning the apparatus. More particularly, the present invention relates to a process for producing a light-receiving member suited for its application in light-receiving members for electrophotography, a deposited film forming apparatus used to produce the light-receiving member, and a method for cleaning the apparatus.
2. Related Background Art
Copying machines, facsimile machines, printers and so forth that utilize electrophotography have been put into wide use. In these electrophotographic systems, it is common to form a toner image by utilizing a light-receiving member having a sensitivity to light, and transfer the toner image to a recording medium.
Photoconductive materials capable of forming photoconductive layers in light-receiving members used in the field of such image formation are required to have properties such that they are highly sensitive, have a high SN ratio [photocurrent (Ip)/dark current (Id)], have absorption spectra suited to spectral characteristics of electromagnetic waves to be radiated, have a high response to light, have the desired dark resistance and are safe to human bodies when used. In particular in the case of electrophotographic light-receiving members set in electrophotographic apparatus used in offices the above safety in their use is an important point.
Photoconductive materials recently attracting notice from such a viewpoint include amorphous silicon (hereinafter "a-Si") (for example, U.S. Pat. Nos. 4,265,991 and 4,552,824 disclose its application in electrophotographic light-receiving members), and are put into practical use as materials for electrophotographic light-receiving members.
Various improvements or proposals are made on the electrophotographic light-receiving members utilizing the a-Si.
These techniques have brought about further improvements in electrical, optical and photoconductive properties, service environmental properties and durability and also have made it possible to improve image quality levels. Such a-Si electrophotographic light-receiving members can be formed by a process including plasma-assisted CVD utilizing glow discharge (hereinafter simply "plasma-assisted CVD").
In spite of originally high durability of a-Si photoconductive layers, it is also known to further form a surface layer (protective layer) on an a-Si photoconductive layer as a technique that can achieve more improvements in the electrical, optical and photoconductive properties, service environmental properties and durability. For example, Japanese Patent Application Laid-open No. 57-115551 discloses an example in which the surface layer is deposited by high-frequency plasma-assisted CVD, decomposing starting material gases by the use of electromagnetic waves with a frequency of 13.56 MHz to cause glow discharge.
To achieve improvements in properties in respect of electrical, optical and photoconductive properties such as dark resistance, photoconductivity and light-response and service environmental properties such as moisture resistance, and also in respect of time stability, Japanese Patent Application Laid-open No. 57-11556 also discloses a technique in which a surface barrier layer formed of a non-photoconductive amorphous material containing silicon atoms and carbon atoms is provided on a photoconductive layer formed of an amorphous material mainly composed of silicon atoms.
Japanese Patent Application Laid-open No. 62-168161 also discloses a technique in which a material comprised of an amorphous material containing silicon atoms, carbon atoms and 41 to 70 atomic % of hydrogen atoms as component elements is used to form the surface layer.
Such layers of a-Si electrophotographic light-receiving members can be formed by a process including glow discharge plasma-assisted CVD as mentioned above, where it is common to use RF plasma-assisted CVD which comprises decomposing starting material gases by the use of electromagnetic waves with a frequency of 13.56 MHz to cause glow discharge.
In recent years, a method of forming deposited films by microwave plasma-assisted CVD making use of a microwave with a frequency of 2.45 GHz as a source for decomposing starting material gases has attracted notice for its industrial application and has been put into practical use (see, for example, Japanese Patent Application Laid-open No. 60-186849).
Such a technique has made it possible to provide electrophotographic light-receiving members having better electrical properties.
Incidentally, in recent years, with spread of high-speed copying machines, digital copying machines and full-color copying machines, electrophotographic apparatus are sought to achieve higher image quality, higher speed and higher durability. As a result, electrophotographic light-receiving members are now required to be more free from memory or faulty copy than ever and, in addition to further improvements in electrical properties or photoconductive properties, to raise charge performance to a level required when used at a high speed and at the same time achieve a great improvement in durability.
For the purpose of service-cost saving, it is also required to improve reliability of component parts so that maintenance requires less time. Under such circumstances, electrophotographic light-receiving members are now so designed that repeated use can be continued for a much longer time than ever in various environments without servicemen's maintenance service.
However, even under such circumstances, the fact is that there is room for further improvements in conventional electrophotographic light-receiving members.
For example, when images are repeatedly formed, sometimes residual images caused during exposure in the course of copying (called blank memory when it is caused by blank exposure) appears in images, or that which is called "ghost", which is a phenomenon in which an image once formed remains as a residual image in the subsequent image formation, is formed on drums having been used at a high speed for a long time.
Such blank memory and ghost are steadily decreasing on account of various improvements having been hitherto made, but the improvements are still unsatisfactory considering that higher image quality and higher-speed copying will be required more and more in the future.
When copying machines are used under higher-speed conditions for a long time, what are called black lines has sometimes occurred, which are black lines appearing on halftone images along the peripheral direction of electrophotographic light-receiving members.
When images are repeatedly formed at a high-speed, it has also often happened that, because of an unsatisfactory uniformity of films formed in electrophotographic light-receiving members obtained by conventional film forming methods, an image density unevenness occurs and conspicuously appears as what is called coarse images, which is ascribable to uneven density of minute images particularly in halftone images. Besides the minute unevenness such as coarse image, uneven density on the whole halftone images may also occur.
When images are repeatedly formed at a high-speed, what is called "white dots" may also occur, which are white small spots on copied images caused, because of an unsatisfactory durability of electrophotographic light-receiving members obtained by conventional film forming methods, and there is a tendency of a gradual increase in its occurrence.
When machines are repeatedly used at a very high speed for a long time, fine lines of images may become blurred (to form smeared images), and, in an extreme instance, images become so coarse that printed letters can not be read at all. Hitherto, smeared images occurring in an environment of high humidity have been prevented by heating a light-receiving member so that the relative humidity on the surface of the light-receiving member is decreased. However, when used under the highest-speed conditions that have ever been experienced, the smeared images can not be prevented on some occasions even if the photoconductive material is heated. Thus, in the development of high-speed copying machines, it is strongly sought to improve light-receiving members also.
Moreover, in electrophotographic apparatus making use of electrophotographic light-receiving members that have once caused such a phenomenon, the occurrence of smeared images often does not stop even if the apparatus are restored to an environment of a relatively low humidity in which no smeared images have ever occurred at all. Hitherto as stated above, smeared images occurring in an environment of high humidity have been prevented by heating a light-receiving member so that the relative humidity on the surface of the light-receiving member is decreased. However, solving the problem by this method makes it necessary to make the drum surface temperature very high, bringing about the problem that the cost of apparatus increases and the consumption of electricity increases.
As a phenomenon different from the one ascribable to humidity, smeared images may also occur when light-receiving members are subjected to high-intensity exposure. This is caused by the disturbance of latent images formed on the surface of an electrophotographic light-receiving member because of charges flowing in the lateral direction in the electrophotographic light-receiving member. The problem of the smeared images that may occur in this way has been almost completely resolved in conventional use by, for example, greatly decreasing oxygen contained as impurities. In the future, however, further improvements should be made when an advance is made toward ultra-high image quality or studies are made on equipment for high image quality full-color copying machines, and this can be regarded as a problem to be solved. This problem is herein called high-intensity exposure smeared images.
Meanwhile, in addition to the above subjects mainly concerned with copied images, it is also sought to more improve potential characteristics such as photosensitivity.
In the amorphous silicon electrophotographic light-receiving members, there is also a problem of potential shift. The potential shift refers to a phenomenon in which the dark-portion surface potential of an electrophotographic light-receiving member changes immediately after charging changes several minutes thereafter, and includes "rise" that indicates an increase in potential and "drop" that indicates a decrease in potential. This appears as a phenomenon in which he density of a copied image on the first sheet becomes different from that on a sheet after continuous copying when copying machines are used. Hitherto, the potential shift has been eliminated by layer configuration designed utilizing the tendency that the rise occurs in a-Si and the drop occurs in a-SiC. In such a case, however, other performances (e.g., ghost) may also change. It is difficult to simultaneously improve the different performances, and it has been sought to make complete improvements.
In the achievement of high-speed copying that is nowadays strongly demanded in the market, charge currents must be increased in order to obtain latent image potential required at the development position. For example, merely increasing charge current density as a means for increasing charge currents results in a serious contamination of a charger which brings about the problem that maintenance must be conducted at shorter intervals. As other means therefor, one may contemplate a method in which the width of a charger is made larger so that charge currents can be increased without changing the charge current density. In such a case, however, it becomes impossible to achieve an other demand in the market, i.e., to make copying machines small-sized. Under such circumstances, it is also strongly sought to improve charge performance of an electrophotographic light-receiving member. Achievement of this improvement in charge performance makes it unnecessary to increase charge currents when high-speed copying is carried out, and to obtain the required latent image potential without causing the problems as discussed above.
When copying machines are used at higher speeds for a long time, a toner may melt-adhere to the surface of an electrophotographic light-receiving member because of sliding friction between a cleaning blade and the surface of the electrophotographic light-receiving member, often causing black dots around imagewise.
Incidentally, as device members used in semiconductor devices, electrophotographic light-receiving members, image input line sensors, image pick-up devices, photovoltaic devices and other electronic devices, deposited films for semiconductors comprised of an amorphous material such as amorphous silicon or amorphous silicon compensated with, e.g., hydrogen and/or a halogen are proposed, many of which have been put into practical use.
Some of these devices have a problem with respect to cost of manufacture. For example when electrophotographic light-receiving members are produced, films must be formed in a relatively large thickness, and necessarily require a long deposition time, resulting in a high cost for their manufacture. Hence, it is sought to provide a deposited film forming apparatus capable of improving efficiency in various aspects concurrently with an improvement in productivity.
As a deposited film forming apparatus for overcoming problems of this type, an apparatus is proposed in which deposited films are formed by plasma-assisted CVD making use of microwaves, as disclosed in Japanese Patent Application Laid-open No. 60-186849. In this apparatus, a plurality of cylindrical members are arranged in a deposition chamber to form an internal chamber, and starting material gases are fed internally so that gas utilization efficiency can be enhanced and at the same time the productivity can be improved.
Since, however, in the case of the above deposited film forming apparatus the microwaves are introduced from the top and bottom of the internal chamber (both ends of each cylindrical conductive substrate), non-uniformity may occur in properties in the general:fix direction of the cylindrical conductive substrate, making it difficult to make the characteristics of deposited films uniform between cylindrical conductive substrates. Such non-uniformity in characteristics has an influence on the yield, and hence has been a factor that brings about a cost increase of devices thus manufactured, even if production efficiency has been improved.
Thus, in the deposited film forming apparatus, it is sought to further satisfy all the gas utilization efficiency, productivity and uniformity characteristics.
In the deposited film forming apparatus as described above, reaction products are partly deposited, or adhere in the form of powder, to portions other than the target substrates, i.e., inner walls and so forth of the reaction chamber. Such deposits or powder may be peeled off and fly to adhere to the surfaces of the substrates to cause, for one thing, film defects such as pinholes in deposited films. Hence, it is necessary to clean inner walls and so forth of the deposited film forming apparatus after deposited films have been formed.
As a method for cleaning a deposited film forming apparatus to remove such reaction products having adhered to the inside of the reaction chamber, a method is known in which the reaction products are removed by using a mixed gas of carbon tetrafluoride (CF.sub.4) and oxygen (O.sub.2), as disclosed in U.S. Pat. No. 4,529,474 and Japanese Patent Application Laid-open No. 59-142839. The former U.S. Pat. No. 4,529,474 discloses that the method is used to remove polysilane having adhered to the inner walls of a reaction chamber in which amorphous silicon deposited films are formed, and the latter Japanese Patent Application Laid-open No. 59-142839 discloses that the method is also effective for cleaning the inside of a reaction chamber in which silicon carbide films are formed.
Japanese Patent Application Laid-open No. 2-77579 also discloses that ClF.sub.3 gas is effective for cleaning a deposited film forming apparatus. This publication also discloses that reaction products having adhered to the inside of a reaction chamber as a result of formation of deposited films are removed by using ClF.sub.3 gas and the deposited film forming apparatus is cleaned while feeding discharge energy of RF plasma (frequency: 13.56 MHz) and microwave plasma (frequency: 2.45 GHz).
As previously stated, in recent years, with the proliferation of high-speed copying machines, digital copying machines and full-color copying machines, electrophotographic apparatus are sought to achieve higher image quality, higher speed and higher running performance. As a result, as previously stated, it is sought to make image quality higher than ever in amorphous silicon drums.
The formation of amorphous silicon deposited films, however, is also accompanied by generation of deposits and products deposited, or adhering in the form of powder, to the inner walls of a reaction chamber. Such deposits or powder may be peeled off and fly adhere to the surfaces of the substrates to cause film defects such as pinholes in deposited films, resulting in occurrence of faulty images.
Various improvements have been hitherto made in order to decrease such faulty images, and have accomplished a reasonable decrease. However, with the advance to higher image quality attributable to electrophotographic apparatus, it is sought to more than ever reduce faulty images.
Although the amorphous silicon drums are enjoying a reasonable cost decrease by virtue of the techniques seen in proposals on their production using microwave plasma-assisted CVD, they are still expensive and further efforts must be made.
Under such circumstances, the fact is that in the field of the production of conventional amorphous silicon drums there is room for further improvements for achieving further cost decreases.
In addition, under the existing conditions, it is urgently sought from an industrial viewpoint to establish a method by which the electrophotographic light-receiving members having solved the problems as discussed above can be produced with good reproducibility of various characteristics, i.e., a good yield, and at a low cost.